Cheerless poet in retrospect (4)
I believe the answer is:
drab
'cheerless' is the definition.
(I've seen this before)
'poet in retrospect' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'in retrospect' shows that the letters should be reversed in order.
'bard' in reverse letter order is 'DRAB'.
(Other definitions for drab that I've seen before include "Lacklustre" , "Dull light brown colour" , "woman with slatternly habits" , "Dowdy" , "Gloomy" .)